This invention relates generally to a switch which is responsive to an ambient temperature level.
The invention more particularly relates to an unresettable switch which will open a circuit when the ambient temperature around the circuit is increased to a predetermined level.
Switches of the type described have become necessary to protect various circuitry in devices such as appliances, etc., from the hazards of high temperatures generated therein. An increasing awareness of the hazards that present themselves as a result of a device which is capable of generating unchecked levels of heat emphasizes the importance of incorporating thermal switches in such devices. Not only destruction to the device but to the immediate surroundings could possibly be eliminated through the use of a switch which is capable of accurately sensing the increase in ambient temperature level to a predetermined amount and quickly and reliably opening the circuit to stop the flow of current therein.
Prior art devices of the type described are generally multi-piece units with a conductive casing. The multi-piece devices of the prior art are inherently costly to produce with a high level of quality control. One such prior art device utilizes a pair of coaxially arranged conductor wires, one of which is electrically connected to an outer conductive casing and the second of which is placed in releasable contact with the conductive casing through a thin washer member. The washer member is urged into contact with the second conductor wire through a spring and a thermal pellet. When a predetermined temperature level is reached, the thermal pellet liquifies, thus releasing the spring energy and allowing a secondary spring to force the washer out of contact with the second conductor wire. Such a device has approximately eight to ten different elements not including the conductor wires.
It is the primary object of the invention to provide a thermal switch device with a minimum of elements.
A further object of the invention is to provide a thermal switch device which is capable of quickly and reliably opening a circuit at a predetermined temperature level.
A still further object of the invention is to provide a thermal switch device which reduces arcing between contact points as the switch is opened.
Still a further object of the invention is to provide a thermal switch device which provides a generally constant cross-sectional area in the current carrying elements to minimize hot spots in the circuit.
A particular advantage of the present invention is the provision of a thermal switch device which is encased with a nonconductive material which facilitates the x-ray inspection of such a device.
The above and other objects and advantages are achieved by the present invention which basically provides for the encapsulation of contact regions of conductor wires, when spring loaded into contact with each other, with a heat fusible material, such as an appropriate organic mixture, followed by a coating or encapsulation of a rigid insulating material providing a structural and protective encasement for the circuitry while insulating the conductor wires from one another except at the contact region. The spring energy is provided in the system by forming a section of at least one of the conductor wires, adjacent the terminal extremity and below a spring hinge region, away from and out of line with the conductor wire section above a spring hinge region. A localized contact region is provided below the spring hinge region so that contact regions may be forced together into electrical contact by a slight, lateral compression force and dipped or encapsulated in a heat fusible material, followed by a second compressive force to load the spring while dipping or encapsulating the contact region in a similar heat fusible material. The heat fusible material will be encapsulated with a rigid insulating material to structurally support the circuit. The encapsulated region will thus provide a closed circuit until the fusible material flows releasing the energy stored in the spring.